Deep Cryogenic Treatment Chamber for Industrial Applications

ABSTRACT

Apparatus and method for construction of a rectangular deep cryogenic treatment chamber using an insulated, steel structure capable of large size and large volume cold thermal treatment. Apparatus includes end or top-mounted closure, liquid nitrogen delivery and distribution mechanisms, fan motors, cold diffusion-less thermal exchange, external heating element, electrical wiring and machined components. The design facilitates both low temperature, dry vapor thermal processing of metal and metal-matrix components down to −320° F. to enhance wear, corrosion, mechanical, thermal and electrical characteristics, and also post-cryogenic tempering capability to 300° F. The apparatus describes an external, LN2 storage dewar and solenoid-activated, gravity fed cryogen delivery via distribution hubs and distributed flow tubes. The apparatus also describes integrated deep cryogenic treatment authentication, test, validation and certification equipment. The process and method of treatment results in certification documents that authenticate and confirm treatment of the subject parts, reflect test and measurement of improved characteristics, retained data for archival purposes and to provide scientific evidence and proof of such treatment to a third-party not present at time of treatments, test or certification

FIELD

Embodiments of the present invention relate generally to apparatus involved in cryogenic and deep cryogenic treatment of materials and, more particularly, to deep cryogenic treatment of large size and large volume items for industrial applications.

BACKGROUND

Deep cryogenic treatment (DCT) of metal articles to enhance wear life has been performed since the 1940's. Early experiments involved quick immersion of die sets directly in a liquid nitrogen (LN2) bath. Those items that did not immediately thermal crack from the 400° temperature differential survived and many exhibited significantly longer life and resistance to fatigue, impact and wear. It was later discovered that a slow ramp down in temperature and a prolonged exposure to dry liquid nitrogen vapors is preferable over direct wet immersion.

DCT is a cold, diffusionless-thermal process that takes 20-50 hours to complete and permanently imparts wear, corrosion and fatigue resistance to metals and metal-matrix items.

Over the last 70 years, improvements to low temperature cryogen delivery systems, PID controllers and thermal processing techniques have made the process reliable, however, DCT has only received limited commercial acceptance due to:

-   -   lack of engineering standards or methods for authentication,         test and process validation     -   historical use of and reliance only on heat treatment to         increase metallic hardness     -   prior to U.S. Pat. No. 9,721,258 issued August 2017, there was         no science-based validation or certification procedure available         for confirming DC treatment in parts using known ASTM test         methods     -   current and historical availability of only small size and         volume DC treatment tanks

The largest available commercial DC treatment chambers are approximately 3′×3′×6′ rectangular or 3.5′×5′ round. The maximum recommended load weight is approx. 5,000 pounds. None of the machines, service providers or treatment facilities perform or provide test, measurement, validation and/or certification services on-site, or at time of DC treatment, for items so treated.

None of the current equipment provides authentication of treatment or standards-based traceability for treated parts, nor do the equipment or service providers supply engineering test data to customers seeking actual confirmation of treatment or proof of levels of performance improvement. A simple anecdotal statement or a payment receipt for services rendered is all that is supplied, in lieu of any formalized testing, authentication or certification against ASTM or industry-accepted standards.

The rectangular machine designs (see 0005) employ either direct immersion of a part in liquid nitrogen, partial dry gaseous exchange or surface exposure via liquid droplets from adjacent spray bars or a combination of these techniques (U.S. Pat. No. 5,865,913 issued February 1999 to Paulin et al; U.S. Pat. No. 5,259,200 issued Nov. 1993 to Karmody). These methods promote quick treatment of parts via rapid exposure of parts to a −320° F. liquid—a condition and technique that can induce thermal shock and metallurgical stress and can also result in subsurface cracking, shortened item life and corrosion formation. These machine designs are not capable of needed post-DCT tempering in-situ and, therefore, users of these equipment designs must perform tempering heat treatment using additional apparatus.

The round chamber (tank) design employs a dry vapor liquid nitrogen atmosphere, contained in a vacuum insulated round chamber, for non-stress inducing thermal exchange (U.S. Pat. No. 5,174,122 issued December 1992 to Levine).

However, both the round and rectangular designs only permit limited weight and volumetric capacity per lot treatment—essentially precluding widespread use of this technology in industrial or commercial applications, or in any scalable application such as is required in the mining, oil and gas, power generation, locomotive or automotive industries. Currently, the available equipment primarily serves the hobbyist, academic, research or small volume markets such as machine tooling, firearms, motor sports or electronics.

Another obstacle to large scale DC application is the volume of supplied liquid nitrogen (LN2) required for treatment of large lots. Most DCT service providers purchase small volumes of LN2 (sufficient to perform a single DC treatment) in 230 litre easily transportable containers. provided by such commercial gas suppliers as Linde, Air Liquide, Praxair or General Air. LN2 delivered in this manner is a low cost, variable expense that requires no large physical space, storage requirement or dedicated flow control equipment. A large chamber for industrial applications could require 10,000 litres or more of liquid nitrogen to perform a single treatment. This type of operation requires significant physical space, material handling capability, cryogen production and/or storage—beyond the financial and operational ability of small DCT service providers.

The lack of a large size DCT chamber with in-situ tempering capability, integrated part authentication and validation equipment, scaled specifically for industrial use, is a key obstacle to widespread adoption of deep cryogenic technology to address wear, corrosion and fracture issues in metal and metal-matrix parts.

BRIEF SUMMARY

Among other things, embodiments herein provide apparatus and methods to deep cryogenically treat large size and weight metallic items in a fixed or portable location; above, in-ground or at ground level.

Embodiments describe cold temperature thermal apparatus that is directly linked to a Programmable logic controller (PLC) or computer with active feedback software and hardware

Embodiments also describe one or more LN2 storage tanks, an on-site or remote liquid nitrogen generator and flow control equipment to deliver LN2.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described in conjunction with the appended figures:

FIG. 1 illustrates the primary components and assemblies relevant to the subject invention.

FIG. 2 illustrates the large size deep cryogenic chamber (tank)

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, one having ordinary skill in the art should recognize that the invention may be practiced without employing one or more specific details. In some instances, geometry, configuration, techniques and manufacturing details have not been shown to avoid obscuring the present invention.

Numerous DCT chamber designs exist in prior art. All are single chamber, rectangular, square or round in shape. They use simple programmable logic controllers (PLC) and are not system linked to any means of authentication, test, validation or certification apparatus. Some of these designs are described in U.S. Pat. No. 3,891,477 issued June 1975 to Lance and U.S. Pat. No. 4,739,622 issued April 1988 to Smith.

None of the present designs utilize treatment information acquired from a test-based, scientific materials database and archive, compare or contrast results against prior material treatments. None of the designs, current or otherwise, known to this inventor, utilize parametric software that combines dynamic treatment, test and engineering analysis to upgrade improvement modifications in treatment protocols.

None of the commercially available deep cryogenic machines, known to this author, are able to treat a part or items larger than 4′×4′×6′, or treat any loads or single parts exceeding 5,000 pound weight. None of the current manufactured DC equipment is able to authenticate, test, validate or certify part treatment in accordance with ASTM or qualification standards for 3rd party certification.

FIG. 1 drawing outlines the present invention of the large format deep cryogenic treatment tank and operational system. The primary components are:

-   -   Liquid Nitrogen generator     -   LN2 storage tank     -   DCT tank     -   computer and software controlling cryogen flow and system         operation     -   digital authentication of treatment (load sheet data page in         software)     -   test equipment validating treatment     -   certification items needed to certify treatment

Liquid Nitrogen is supplied to one or more LN2 storage tanks, via an on-site or off site liquid nitrogen generator, directly linked to the DCT chamber. Normally, such storage tanks are dual wall, vacuum jacketed and supply LN2 between 125-250 psi. They can be vertical or horizontally mounted and are usually placed on a concrete pad, engineered to support tank weight when full.

FIG. 2 illustrates a cutaway side view of the rectangular DC treatment chamber. Embodiments of this invention describe a large steel chamber— some portion on, in or located below ground level, with either 1) vacuum insulated wall sections backed by inner and outer facing skins, 2) non-vacuum insulated wall sections backed by inner and outer facing skins, 3) expanded glass, polyisocyanurate, polyurethane, fiberglass, mineral wool, blown-in expanded or semi-solid insulation membrane backed by inner and outer facing skins. Appropriate insulation vapor barriers and multiple layer sealing may be required as per a manufacturer's engineering instructions. Roof or side wall-mounted pressure relief valves or dampers are installed to maintain under 14.7 psi maximum constant internal chamber pressure at sea level.

The term ‘facing skins’ may refer to any stainless steel, galvanized, aluminum, metal-matrix or metallic sheet metal—welded, brazed, riveted, lapped, screwed, bolted, assembled or fabricated—that is used to provide either or both a sealing surface and an additional reflective and/or insulating layer to reduce thermal exchange and inhibit thermal transport.

The chamber may rest on one or more vapor barriers, leveling pads and/or insulation mats which can prevent thermal loss, condensation, moisture wicking and damage to the floor or concrete underlayment.

The entire deep cryogenic chamber is capable of handling up to 60,000 lbs total aggregate weight and may be sub-dividable into one or more chambers—each independently controlled and capable of staggered or simultaneous cryogenic and/or tempering, treatment or processing cycles—with respect to the treatment cycle operating in an adjacent (subdivided) tank chamber.

The loading and unloading of large components into the chamber may be accomplished by hand, robot-assisted, roller rail or crane/hoist assist, while small components may be loaded as described above or off-line pre-loaded into custom built containment cages that facilitate more orderly and rapid logistics flow. The use of custom containment cages also simplify lot authentication, RFID tracking and verification and assist in segregating and processing quantities that require specific contract-stated control of material.

Regardless of loading method, all DC treatment described by this invention may utilize procedures outlining authentication, material control, validation, test, measurement and certification of materials. Such methods and procedures may include one or more of the following: transducer and thermocouple-based direct part temperature sampling, active feedback and protocol recalibration at flow controls, sensor-based data acquisition, time/date stamping for authentication, use of part-affixed strain gages for part/lot treatment authentication, archival data storage, use of statistically valid baseline and witness proxy artifacts for destructive testing and non-destructive residual stress and/or retained austenite testing using X ray diffraction for validation and certification.

FIG. 2 illustrates one embodiment or configuration of the chamber. Regardless of volume occupied by treatment payload, the chamber will be sealed by door closures that seal on felt, insulating material or sealing strips, located around the tank end lid perimeter. Corner or rim-mounted magnetic relays electronically confirm lid closure to the DC treatment software to allow a safety confirmation before start of a treatment cycle.

The chamber operates using solenoid-activated, gravity fed cryogen delivery via distribution hubs with individual distribution flow tubes running along the side or back walls—either having percolation holes running along some portion of the tube length or unperforated walls until termination at open ends or a combination thereof. Fabricated heating ducts, to channel on-demand propane or natural gas supplied tempering heat, are mounted to the tank structure. Cryogenically-rated hardware and hose link the solenoid-controlled LN2 distribution hubs to the LN2 source and permits rapid connect/disconnect.

As seen in one embodiment in FIG. 2, LN2 is piped from the LN2 storage tank into the DCT chamber distribution hub where it moves into the connected flow tubes. As the liquid phase nitrogen travels through the flow tubes, ambient warm air in the chamber triggers a thermal exchange and the −320° F. liquid nitrogen boils. Turning into nitrogen vapor at just over −320° F., the LN2 expands at a 1:694 rate, thus exerting gas pressure through each flow tube. The cold but dry nitrogen vapor accelerates thermal exchange and allows a calculated and metered temp drop in the retained heat of the payload. This portion of the DCT cycle is called the ‘ramp down’ phase. The ramp down phase is often accompanied by use of 1 or more powered fan and blowers to facilitate even dispersion of dry cold vapor within the chamber.

FIG. 2 illustrates the dry LN2 vapors encountering the payload, forcing thermo-kinetic thermal exchange and causing additional liquid nitrogen to boil. After an 8-20 hour period, final treatment temperature is reached at approx. −302° F. and the cold chamber temperature is maintained for a period of 6-20 hours—as necessary per specific treatment recipe to induce permanent, grain-level metallurgical changes in the lot of part(s) and impart the desired benefits. This portion of the DCT cycle is called the ‘dwell’ phase.

Following the dwell phase, LN2 flow is halted and the payload temperature slowly returns to ambient temperature due to a combination of a) thermal exchange from temperature differential between internal and external chamber temperatures, and b) the introduction of heat through ducted plenums by external forced-air propane or natural gas-fired torpedo heaters. The chamber temperature slowly increases the payload temperature over an 8-16 hour period until it reaches equilibrium by matching the external chamber ambient temperature. This portion of deep cryogenic treatment is called the ‘ramp up’ phase.

By conducting the ‘ramp up’ or warming phase in a semi-sealed chamber without introducing external, moisture-laden air, condensation and corrosion formation at dew point exchange is avoided. When the payload reaches ambient temperature, the heat cycle continues and between 1-3 tempering cycles to a maximum of 350° F. are conducted. These 2-8 hour tempering cycles are necessary to remove hydrogen embrittlement from certain materials and to increase post-DCT ductility. This portion of the DCT cycle is called the ‘tempering’ phase.

The flow control device illustrated in FIG. 1 provides time and temperature delivery of LN2 according to deep cryogenic treatment recipes. These recipes match and maximize the deep cryogenic improvement to wear, fatigue, fracture, tensile, yield strength, corrosion resistance and other metallurgical benefits for each material. Since each material and alloy vary, as well as the optimization protocol specific for each application (eg—creep for hot section turbine blades, fatigue for electrical vehicle gears, fracture for blowout preventer hardware, corrosion for deep water/subsea drill components), complex proprietary software is dynamically generated and reinforced through testing conducted on representative artifact witness samples that accompany each and every lot of materials that is DC treated. 

What is claimed is:
 1. Apparatus for performing deep cryogenic treatment and processing of metal and metal-matrix materials to permanently improve mechanical, electrical, chemical or physical characteristics. This apparatus comprises A metal DC treatment chamber that is rectangular in shape and sub-dividable into one or more chambers Chamber construction from steel alloy with one or more liners that may be vacuum sealed and/or insulated The chamber located above, below or partially in-ground, with a minimum treatment weight capacity of 5,000 pounds. Chamber loading to be accomplished by hand, remote robotic, by crane, hoist, rail, track or tramway assist.
 2. Apparatus and method in claim 1 wherein: Each chamber contains the thermo-mechanical components necessary to induce and complete both low and high temperature thermal treatments called respectively deep cryogenic treatment and tempering. The chamber is a thermal exchange chamber containing distribution hubs, wiring, sensors, fans, blower motors and flow tubes LN2 is introduced, controlled and precisely metered from a computer-based flow device The LN2 is stored in storage vessels The LN2 is produced using an on-site or off-site liquid nitrogen generator
 3. Apparatus and method in claim 2 wherein: Authentication of DC treatment is provided via non-destructive or destructive test equipment and methods. Proxy witness artifacts may be included in each DCT lot and archival storage, testing and certification can happen on-site or at a remote location. Authenticated parts can be tested, validated and certified using strain gages, X-ray diffraction or other known ASTM methods and standards 